--- a/2023/leakyroof.ml	Wed Dec 13 09:34:10 2023 +0100
+++ b/2023/leakyroof.ml	Wed Dec 13 15:02:07 2023 +0100
@@ -22,12 +22,16 @@
 
   type cover = { rows : bool array; cols : bool array } [@@deriving sexp]
 
+  (* Memory for covered rows/columns. Runtime and memory efficient: no copies
+     necessary, just some bits set temporarily. *)
   let cover_for_roof roof =
     {
       rows = Array.create ~len:roof.m false;
       cols = Array.create ~len:roof.n false;
     }
 
+  (* Execute function f while row m is covered in cover.
+     Restore previous state after f returns. Return f's result. *)
   let with_row_covered m cover f =
     let old = cover.rows.(m) in
     cover.rows.(m) <- true;
@@ -65,6 +69,7 @@
     Array.find_mapi roof.a ~f
 end
 
+(* Recursive optimal solution guaranteed *)
 let rec solve roof cover =
   match Roof.first_open_leak roof cover with
   | None -> Roof.covers cover